Recently, a relationship between D-serine and psychiatric disease, particularly schizophrenia, has been pointed out. For example, it has been reported that the D-serine concentration is low in both the serum and cerebrospinal fluid of schizophrenic patients (non-patent document 1, non-patent document 2). Moreover, it has been reported that the combined use of D-serine and existing antipsychotic drugs improves positive symptoms, negative symptoms and cognitive function in schizophrenic patients (non-patent document 3).
D-serine is produced from L-serine by serine racemase, and metabolized by D-amino acid oxidase (DAAO). Since DAAO is widely distributed in the brain (non-patent document 4), it is expected that the intracerebral D-serine concentration will be increased and the cognitive function will be improved by inhibiting DAAO.
In addition, DAAO produces, along with the D-serine oxidation, reactive oxygen species such as hydrogen peroxide, which are toxic metabolites. Reactive oxygen species are known to participate in neuropathic pain such as hyperalgesia and the like (non-patent document 5). Furthermore, the above-mentioned toxic metabolite may cause neuron injury. Therefore, inhibition of DAAO is considered to be useful for psychiatric diseases including schizophrenia and bipolar disorder, diseases damaging learning and memory such as Alzheimer's disease, Parkinson's disease, Huntingdon's disease and the like, and further, neuropathic pain and neurodegenerative diseases.
Benzoic acid is known as a DAAO inhibitor (non-patent document 6), and it is known that benzoic acid suppresses hyperalgesia, alllodynia, and neuropathic pain (non-patent documents 7, 8), and other DAAO inhibitors suppress alllodynia in a neuropathic pain model (patent document 1, patent document 2), and learning⋅memory⋅dementia (patent document 3).
Some compounds having a DAAO inhibitory action have been reported and, for example, a compound represented by the following formula (A) can be mentioned (non-patent document 9).

In addition, a pyrrole carboxylic acid derivative (patent document 1, patent document 2) has been reported to show a DAAO inhibitory action.